21778740 has 96 divisors (see below), whose sum is σ = 69995520. Its totient is φ = 5616000.

The previous prime is 21778727. The next prime is 21778763. The reversal of 21778740 is 4787712.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21778695 and 21778704.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16090 + ... + 17390.

It is an arithmetic number, because the mean of its divisors is an integer number (729120).

Almost surely, 2^21778740 is an apocalyptic number.

21778740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21778740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34997760).

21778740 is an abundant number, since it is smaller than the sum of its proper divisors (48216780).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21778740 is a wasteful number, since it uses less digits than its factorization.

21778740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1350 (or 1342 counting only the distinct ones).

The product of its (nonzero) digits is 21952, while the sum is 36.

The square root of 21778740 is about 4666.7697607660. The cubic root of 21778740 is about 279.2614037517.

The spelling of 21778740 in words is "twenty-one million, seven hundred seventy-eight thousand, seven hundred forty".